1. Field of the Invention
The present invention relates to an ophthalmic apparatus including an eye refractive power measurement apparatus and a cornea shape measurement apparatus and, more particularly, to an ophthalmic apparatus provided with an alignment system, particularly with a suitable constitution for accommodating a working distance of hand-held type apparatus.
2. Description of Related Art
Many ophthalmic apparatuses are installed-type apparatuses, which have conventional alignment system that an examiner directly observes an examinee's eye through an ocular lens-barrel to adjust the alignment of apparatus. The alignment system utilizes indexes projected onto the examinee's eye to detect suitability of the working distance. When the examinee's eye is positioned at a predetermined distance from the apparatus, images of indexes projected on the eye will coincides with each other. The alignment system has advantages in that it is relatively inexpensive and, because of a pure optical system, it enables observation of precision images within a range that resolving power of examinee's eye admits.
An ophthalmic apparatus which is provided with system of imaging an examinee's eye by infrared light and then displaying a visible image of the eye on a TV monitor, has come into wide use recently. In the ophthalmic apparatus, an optical axis adjusted by arranging an image of the examinee's eye, an alignment mark superimposed on the image of the eye and a first Purkinje image formed by a cornea reflection light so that they are positioned with a desired positional relation with each other, and a working distance is adjusted by bringing the first Purkinje image into focus. This alignment system has advantages in that it is not influenced by examiner's diopter, and the examiner can conduct alignment of the apparatus at a distance from the examinee's eye and in a comfortable position accordingly, and others.
In the former apparatus of conventional installed-type, the examinee and the examiner have to come close to each other, causing a problem of giving the examinee an uncomfortable feeling and compelling the examiner to take an unnatural position respectively.
The latter apparatus has also problems that it would be more expensive in cost and larger in size because it needs a television camera and a television monitor. And further, picture quality the latter apparatus provides is inferior than that of the former apparatus.